1. Field of the Invention
The invention concerns a stepping motor for analog display of digitally transmitted values.
2. Description of the Related Art.
This type of stepping motor has attracted a great deal of attention in recent years, particularly in the construction of automobiles, and serves for the analog representation of driving conditions and driver information, wherein digitally measured values, particularly speed, rotations per minute, gas tank volume, oil pressure, etc., are indicated with high resolution. The individual steps must therein be selected to be so small, that the observer cannot recognize these as such, but rather receives the impression of a continuous analog readout. As rule, it is thus preferred to provide the stepping motor with a reduction gear, which translates the angular displacement per step of the rotor in a strongly reduced angular displacement of the drive or, as the case may be, indicator shaft. Conventionally reduction gears with a reduction relationship of 60:1 are employed, which in combination with conventional angular displacements per step provide a sufficient resolution.
In this connection, it is of particular importance, that the step motor is constructed simply and robustly and therewith also economically. Such a stepping motor has been known, for example from DE 42 07 978, which is comprised of two stators which are positioned one above the other and with an angular offset with respect to each other. The stators are herein designed in a shape of a ring and encompass a rotor completely circumferentially, the rotor provided with permanent magnets. The assembly of the completed stepping motor is comparatively simple, since the respective construction elements are successively seated in a housing. Suitable positioning elements adapted to each other insure that the various construction elements are seated in the appropriate orientation. This concerns in particular also the stators, which must indicate the sensed angular displacement.
Disadvantageous herein is the comparatively high expense, which is necessary with respect to the housing and the stators, in order to form the positioning elements. Further, the construction of the two stators has proven itself in particular to be comparatively expensive, since, because of the ring shape of the coils, the stator plate must be specially formed. The coaxial positioning of the two ring shaped stators also results in a relatively high construction height of the stepping motors, which is undesirable for a number of applications. Further, high axial forces occur as a result of this design, causing displacement of the rotor (so-called jumping).
The invention is thus concerned with the problem of providing a stepping motor of the above-described type which no longer exhibits the above-described disadvantages. In particular, a simple construction of a stepping motor should be realized, which makes possible a particularly flat construction.